Rechargeable power supply system and method of protection against abnormal charging

ABSTRACT

An intelligent battery comprising a battery cell for charging and discharging; a voltage detection circuit for detecting voltage of the battery cell; a current detection circuit for detecting charging current; a charging-stop FET for stopping charging for the battery cell; and a CPU for activating the charging-stop FET based on voltage detected by the voltage detection circuit, wherein before the voltage reaches a voltage for activation of the charging-stop FET, when the charging current value detected for the battery capacity by the current detection circuit is larger than a reference, the CPU determines that an abnormal state occurs, and activates the charging-stop FET. The present invention provides, in part, a battery, which is safer even if dual accidental malfunctions occur.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a power supply system having abattery that can be used by repeated charging/discharging (secondarybattery), more particularly, to a power supply system having aprotection facility against abnormal charging.

[0003] 2. Background of Related Art

[0004] In various devices and apparatuses (such as notebook-sizedpersonal computers (notebook PCs), PDAs, information terminal equipmentincluding mobile phones, Mini Disc (MD) drives, and video cameras),secondary batteries are extensively employed as a battery that can beused many times by repeated charging/discharging. As a secondarybattery, often nickel-hydrogen batteries or nickel-cadmium batteries areused, where such use is employed typically since these types ofbatteries are inexpensive and have larger capacity. Additionally, othertypes including lithium ion batteries, having higher energy density perunit weight than the nickel-cadmium batteries, and lithium-polymerbatteries, that uses a solid polymer instead of a liquid electrolyte,may also be used.

[0005] If a secondary battery such as a nickel-hydrogen battery, anickel-cadmium battery, a lithium ion battery, or a lithium-polymerbattery, is in an over-charging state or an over-discharging state,problems such as lowered performance, damaged electrodes, orshort-circuits inside the battery may occur.

[0006] For example, in Published Unexamined Patent Application No.6-86469 (Japan Patent Office) the specification discloses a techniquefor the alarming of short-circuits by generating signals based on thedetection of a lowered battery voltage and short-circuits within thebattery. Additionally, in Published Unexamined Patent Application No.2000-102185 Japan Patent Office), the specification discloses atechnique wherein each secondary battery cell in a first battery groupand each secondary battery cell in a second battery group are connectedseparately for monitoring/controlling purposes, such that if an internalshort-circuit occurs in one of the battery groups, a short-circuitcurrent is prevented from flowing into the secondary battery cells inthe other battery group.

[0007] However, in above-referenced Published Unexamined PatentApplication Nos. 6-86469 and 2000-102185 described above andincorporated by reference herein, when an internal short circuit occursin a condition where the battery is charged to a voltage above apredetermined voltage due to a malfunction of the apparatus, it isimpossible to prevent a battery from being in a dangerous state whileshort-circuit current can be prevented from flowing into batteries. As aresult, it is generally known that when an internal short-circuit in abattery cell occurs in addition to overvoltage in the battery, thecondition of the battery becomes dangerous.

[0008] In order to charge a secondary battery (battery-pack) a chargeris often used with an alternating current (AC) adapter. When ashort-circuit breakdown occurs in either a switching transistor in thecharger or a short-circuit prevention transistor for preventingshort-circuit in the charger, the AC adapter and the batteryshort-circuit electrically, resulting in an abnormal charging of thebattery (first error). In this case, charging continues until a primaryprotection circuit in the battery pack goes into operation. At thispoint, the battery voltage, for example in the case of lithium-ionbattery, is about 4.35 V/cell. If additionally a short-circuit occurs inthe battery cell, a dangerous state (second error) is possible. Thesedangerous states as well as a situation where the battery is in a hightemperature environment should be taken into consideration in designing.

[0009] Currently, intelligent batteries having a CPU built-in in abattery pack (secondary battery) are widely used. For example, a lithiumion battery constituting an intelligent battery is used, in which acharging stop FET (charging protection circuit) and a discharging stopFET (discharging protection circuit) are built in a battery pack. TheCPU in the battery pack monitors the voltage in the battery by inputtinga signal from a voltage detection circuit, then analog-to-digital (A/D)converting the signal inside it. In this battery pack, when the voltagereached 4.35 V or higher, for example, it is determined that abnormalcharging occurs, and the charging is aborted by turning off the chargingstop FET. Since the battery voltage in full charging (100% charging)state is 4.2 V (±50 mV), the current design in which abnormal chargingis detected at 4.35 V/cell is considered to be proper taking detectionerror and other factors into consideration.

[0010] However, while a safety state can be maintained in a normalcondition, a dangerous state becomes possible, when in a conditioncharged to 4.35 V further occurs a malfunction such as internalshort-circuit in the battery cell. It is therefore necessary toaccommodate the worst case taking conditions such as ambient temperatureinto consideration.

SUMMARY OF THE INVENTION

[0011] The present invention is made to solve and overcome the technicalproblems described above, as well as other known limitations in the art.It is an object of the present invention to provide a battery, which issafer, even where double accidental malfunctions occur.

[0012] An object of the present invention is to operates to maintainsafety, such that when a short-circuit occurs in a battery cell, andwhen the battery is charged to a voltage above a predetermined voltagedue to a malfunction of a connected charger (or a portion of anapparatus), to above charging by detecting a malfunction of the charger(or the portion of the device) before the conventional first overvoltageprotection facility is activated.

[0013] Therefore, in one aspect, the present invention is a power supplysystem with a battery for supplying power to a main system, comprising:charging current measuring means for measuring charging current for thebattery; battery capacity calculation means for calculating(integrating) battery capacity of the battery; detection means fordetecting malfunction occurring in the battery based on a chargingcurrent value obtained and the battery capacity calculated (malfunctionoccurrence detection means); protection facility activating means foractivating a protection facility based on detection of malfunctionoccurrence; and notification means for notifying the main system ofmalfunction occurrence based on detection of the malfunction.

[0014] The detection means (malfunction occurrence detection means) ispreferably adapted, for example, to detect malfunction occurrence basedon information in a table for malfunction detection, showing therelation between battery capacity and malfunction detection currentvalue. The detection means can also be adapted to detect malfunctionoccurrence based on an equation representing the relation betweenbattery capacity and charging current value, which equation isseparately defined according to battery capacity.

[0015] In another aspect, the present invention is also a computerdevice, comprising: a main system for data processing; and anintelligent battery for supplying power to the main system, wherein theintelligent battery comprises: a battery cell for charging anddischarging; a current detection circuit for detecting charging currentfor the battery cell; a CPU for calculating battery capacity byintegrating detected charging current, and recognizing malfunctionoccurrence occurring in the battery based on charging current valuedetected by the current detection circuit and the battery capacitycalculated; and a protection circuit for performing stop operationaccording to instruction from the CPU based on recognition ofmalfunction by the CPU.

[0016] In a further aspect, the present invention may also be understoodto be a battery connected to a main system of a computer device or thelike (intelligent battery). Thus, a battery according to the presentinvention, comprises: a battery cell; a voltage detection circuit fordetecting voltage for the battery cell; a current detection circuit fordetecting charging current for the battery cell; a charging stop unitfor stopping charging for the battery cell; and a control unit foractivating the charging stop unit based on voltage detected by thevoltage detection circuit, wherein before the voltage reaches a voltagefor activating the charging stop unit, the control unit detects anabnormal state based on a charging current value detected by the currentdetection circuit, and activates the charging stop unit.

[0017] In another aspect, the present invention is a method forprotecting a battery from abnormal charging, comprising: measuring acharging current value for the battery; calculating integrated capacityfor the battery; and activating a protection facility when the chargingcurrent value measured for the calculated integrated capacity is largerthan a predetermined value. The method is preferably characterized inthat the protection facility is activated based on information such astable information or an equation, specifying a reference valuerepresenting a charging current value at which a malfunction is detectedfor an integration capacity, since malfunction occurring can be detectedas soon as abnormal current for an integrated capacity flows. Theprotection method can also provide a battery with excellent safety sincethe protection facility can be activated in the state where theintegrated capacity is less than 100%.

[0018] In another aspect, a method for protecting from abnormal chargingaccording to the present invention is characterized for example, in thatit comprises: recognizing that a battery is connected to an apparatussuch as a typical notebook PC with a charger forconstant-current/constant-voltage charging, by using ID or the like thatis identification information delivered from the apparatus; measuringcharging current value when the battery is charged while switching fromconstant-current charging to constant-voltage charging, determiningbased on the measured charging current value whether abnormal chargingoccurs or not; and aborting charging when it is determined that abnormalcharging occurs.

[0019] In yet another aspect, the present invention may also beunderstood as programs for enabling in a microcomputer contained abattery to perform each of these functions. The programs can be providedto a microcomputer a processing unit from a remote program transmissiondevice via a network, for example. The program transmission device maybe configured to comprise storage means such as a CD-ROM, a DVD, amemory or a hard-disc with the programs stored therein, and atransmission means for reading the programs from the storage means andtransmitting the programs to a device for executing the programs, viaconnectors and networks such as Internet or LAN. The programs may beprovided by using a storage medium such as CD-ROM.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Other aspects, features, and advantages of the present inventionwill become more fully apparent from the following detailed description,the appended claims, and the accompanying drawings in which:

[0021]FIG. 1 shows a hardware configuration of a computer system towhich an embodiment of the present invention is applied;

[0022]FIG. 2 shows a configuration of an intelligent battery comprisingan abnormal charging protection function according to an embodiment ofthe present invention;

[0023] FIGS. 3(a) and (b) show charging characteristics of a lithium ionbattery;

[0024]FIG. 4 shows a relationship between battery capacity and chargingcurrent in a normal charging;

[0025] FIGS. 5(a) and (b) show an example of determination criteria formalfunction detection used in an embodiment of the present invention;

[0026]FIG. 6 is a block diagram of processes performed in CPU of theintelligent battery;

[0027]FIG. 7 is a flow chart showing process flow in the case where thetable shown in FIG. 5(a) is used; and,

[0028]FIG. 8 is a flow chart showing a flow of abnormal state detectionprocess based on numeral formulas.

DETAILED DESCRIPTION OF THE INVENTION

[0029]FIG. 1 is a diagram showing a hardware configuration of a computersystem 10, for an embodiment of the present invention.

[0030] A computer device comprising this computer system 10 isconfigured as a notebook-size of personal computer (notebook PC) havinga predetermined operation system (OS) loaded therein, preferably incompliance with Open Architecture Developer's Group (OADG)specification, for example.

[0031] In the computer system 10 of FIG. 1, a CPU 11 functions as theoperational brain of the entire computer system 10, and executes variousprograms under the control of the OS. The CPU 11 is interconnected withvarious units via three buses: Front Side Bus (FSB) 12 as a system bus;Peripheral Unit interconnect (PCI) bus 20 as a bus for high speed I/Odevice; and Industry Standard Architecture (ISA) bus 40 as a bus for lowspeed I/O device. This CPU 11 is designed to increase processing speedby storing program codes or data in cache memories. Typically, a SRAM ofabout 128K bytes is integrated in the CPU 11 as a primary cache,although more and less are foreseen by the present invention. However,in order to make up for capacity shortage, a secondary cache 14 of about512K to 2M bytes is connected to the CPU via a Back Side Bus (BSB) 13that is an exclusive bus. It is also possible to eliminate the BSB 13and to connect the secondary cache 14 to FSB 12 so as to avoid use of apackage with many terminals, thereby reducing the cost.

[0032] The FSB 12 and the PCI bus 20 are in communication with a CPUbridge 15 called memory/PCI chip (host-PCI bridge). The CPU bridge 15comprises a memory control function for controlling operation to accessa main memory 16, a data buffer for buffering difference in datatransfer rate between the FSB 12 and the PCI bus 20, and so on. The mainmemory 16 is a writable memory used as an area for reading an executionprogram for CPU 11, or a working area to which process data for theexecution program is written. For example, it consists of several DRAMchips, equipped with a 64 MB chip for example, as its standard, havingcapability of expansion up to 320 MB. The execution program includes OSand various drivers for hardware operation of peripheral devices,application programs intended for specific work, and firmware such asBasic Input/Output System (BIOS) stored in a flash ROM 44 that will bedescribed later.

[0033] A video subsystem 17 is a subsystem for implementing a functionfor video, and includes a video controller. The video controllerprocesses a rendering instruction from the CPU 11 to write the processedrendering information to a video memory, and to read out the renderinginformation from the video memory so as to output it as rendering dataon a liquid crystal display (LCD) 18.

[0034] The PCI bus 20 is a bus that allows relatively high-rate datatransfer, and standardized by a specification with data bus width of 32bits, 64 bits, maximum operation frequency of 33 MHz, 66 MHz, andmaximum data transfer rate of 132 MB/sec, 528 MB/sec. An I/O bridge 21,a card-bus controller 22, an audio subsystem 25, a docking stationinterface (Doc I/F) 26, and a mini PCI connector 27 are connected to thePCI bus 20, respectively.

[0035] The card-bus controller 22 is an exclusive controller fordirectly coupling a bus signal on the PCI bus 20 with an interfaceconnector (card bus) of a card-bus slot 23. A PC card 24 can be insertedto the card-bus slot 23. The docking station interface 26 is hardwarefor connecting a docking station (not shown) that is a functionexpansion device of the computer system 10. When a notebook PC is set inthis docking station, the various hardware units connected to theinternal buses of the docking station are connected to the PCI bus 20via the docking station interface 26. A mini PCI card 28 is connected tothe mini PCI connector 27.

[0036] The I/O bridge 21 comprises a bridge function between the PCI bus20 and the ISA bus 40. It also comprises a DMA controller function, aprogrammable interruption controller (PCI) function, a programmableinterval timer (PIT) function, Integrated Device Electronics (IDE)interface function, a Universal Serial Bus (USB) function, and a SystemManagement Bus (SMB) interface function. The I/O bridge also preferablyhas a built-in real time clock (RTC).

[0037] The DMA controller function is a function for performing datatransfer between peripheral devices such as FDD and the main memory 16without passing through the CPU 11. The PCI function is a function forresponding to interruption request (IRQ) from a peripheral device toexecute a predetermined program (interruption handler). The PIT functionis a function to generate timer signal with a predetermined frequency.An IDE hard-disc drive (HDD) 31 is connected to the interfaceimplemented by the IDE interface, and a CD-ROM drive 32 is ATAPI (ATAttachment Packet Interface) connected to the interface. Instead of theCD-ROM drive 32, another type of IDE device such as Digital VersatileDisc (DVD) drive may be connected to the interface. External storagedevices such as the HDD 31 or the CD-ROM drive 32, are accommodated, forexample, in an accommodation place in a notebook PC body, called “mediabay” or “device bay”. Theses external storage devices equipped as astandard may be installed in an exchangeable and exclusive manner withother devices such as FDD and a battery pack.

[0038] The I/O bridge 21 is provided with a USB port, which is connectedto a USB connector 30 disposed, for example, on a wall surface of anotebook PC body. An EEPROM 33 is connected to the I/O bridge 21 via SMbus. The EEPROM 33 is a memory for storing information such as apassword or supervisor password registered by the user and the productserial number, and is non-volatile, and electrically rewritable forstored content.

[0039] The I/O bridge 21 is also connected to a power supply circuit 50.The power supply circuit 50 comprises an AC adapter 51 connected to acommercial main of AC 100 V, for example, for AC/DC conversion, anintelligent battery 52 as a battery (secondary battery), a batteryswitching circuit 54 for charging the intelligent battery 52 andswitching power feeding paths from the AC adapter 51 and the intelligentbattery 52, and a DC/DC converter (DC/DC) 55 for generating constant DCvoltages used in the computer system 10, such as +15 V, +5 V, and +3.3V. The intelligent battery 52 may removable from the main system as abattery pack, and may also be provided inside the housing of the mainsystem.

[0040] In a core chip composing the I/O bridge 21, an internal registerfor managing a state of the power supply 10, and a logic for managing astate of the computer system 10 including the operation of the internalregister (state machine) is provided. This logic transmits to/receivesfrom the power supply circuit 50, various signals. The logic recognizesthe actual state of feeding from the power supply circuit 50 to computersystem 10 by the transmission/reception of the signals. The power supply50 controls the power feeding to the computer system 10 according toinstructions from the logic.

[0041] The ISA bus 40 is a bus with a data transfer rate lower than thePCI bus 20 (for example, bus width: 16 bits, maximum data transfer rate4 MB/sec). An embedded controller 41 connected to a gate array logic 42,a CMOS 43, a flash ROM 44, and a Super I/O controller 45 are connectedto the ISA bus 40. The ISA bus 40 is also used for connecting peripheraldevices operating in relatively low speed such as keyboard/mousecontroller. An I/O port 46 is connected to the Super I/O controller 45,and controls driving of FDD, input/output of parallel data via aparallel port (PIO), and input/output of serial data via a serial port(SIO).

[0042] The embedded controller 41 controls keyboard (not shown), and isconnected to the power supply circuit 50 to support in part the powersupply management function by means of a built-in power managementcontroller (PMC) in cooperation with the gate array logic 42.

[0043]FIG. 2 shows a configuration of the intelligent battery 52comprising an abnormal charging protection function in the embodiment.The intelligent battery 52, to which the embodiment is applied,comprises in the battery pack a CPU 61 that is a microcomputer toperform processes for abnormal charging protection, a voltage detectioncircuit 63 for detecting voltage of battery cells 62 and notifying theCPU 61, and a current detection circuit 64 for measuring current flowingin the battery cells 62 and notifying the CPU 61. It also comprises adischarging-stop FET 65 (FET3) for protecting the intelligent battery 52in abnormal discharging, and a charging-stop battery FET 66 (FET4) forprotecting the intelligent battery 52 in abnormal charging.

[0044] The CPU 61 inputs a signal from the voltage detection circuit 63,and A/D converts it inside to monitor the battery voltage. For example,in the case of lithium ion battery it is configured such that whenvoltage of the battery cells 62 reached 4.35 V or more per each onecell, it determines that abnormal charging is being performed and abortscharging by turning off the charging-stop FET 66 (FET4). Specifically,since voltage of the battery in full charged state (100%) is 4.2 V (±50mV) per cell, the CPU 61 is adapted to detect abnormal charging at 4.35V/cell in the light of detection error. The CPU 61, by communicationutilizing a communication line (COM1), transmits information aboutdetected abnormal charging to the embedded controller 41 (system-side),and also transmits to/receives from the embedded controller 41(system-side), various types of information such as information aboutbattery capacity or life.

[0045] FIGS. 3(a) and (b) show charging characteristics of a lithium ionbattery. FIG. 3(a) shows a characteristic for normal charging, and FIG.3(b) shows a characteristic for abnormal charging due to a failure. InFIGS. 3(a) and (b), the horizontal axis represents charging time(hours), and the vertical axis represents charging current (mA) andbattery capacity (%) to show battery capacity and charging current. Asshown in FIG. 3(a), in the normal charging, as the battery capacityincrease to a certain value (60% in FIG. 3(a)) or more, the chargerchanges its state from constant current charging to constant voltagecharging, then the charging current decreases. For example, in a typicalcharging manner, when the charging current value reach about 300 mA orless, it is determined that full charging is achieved, then thecharging-stops.

[0046] However, when main system is in power-off state, if ashort-circuit failure occurs in the FET3 or FET4, an abnormal charginglike the one shown in FIG. 3(b) takes place. In the example shown inFIG. 3(b), the AC adapter 51 has a characteristic of, for example, aconstant voltage of 16 V and a constant current of 3.3 A (3300 mA). Whena short circuit occurs, the charging of the battery take place at 3.3 Auntil the charging is aborted, specifically, until the charging isaborted by the-protection circuit (charging stop FET 66), which, whenthe voltage per cell reaches 4.35 V or more, determines that abnormalcharging takes place, then operates. When the main system is inoperation, since the power is also fed to the main system, the chargingcurrent is low, for example 2.0 A, but the charging of the battery alsocontinues until the protection circuit (charging stop FET66) operates.

[0047] Therefore, in this embodiment, the determination of malfunctionoccurrence in the battery is made by taking relationship between thebattery capacity and the charging current.

[0048]FIG. 4 shows a relationship between battery capacity and chargingcurrent during normal charging. In FIG. 4, the horizontal axisrepresents battery capacity (%), and the vertical axis representscharging current (mA). As shown in FIG. 4, as battery capacityincreases, typically, charging current decreases. Accordingly, when toolarge current flows for a battery capacity, it is possible to determinethat a malfunction occurs. Specifically, it is possible to predeterminea current value by which a malfunction is detected, and to detectmalfunction occurrence as soon as the detected charging currentincreases too much for the current value.

[0049] FIGS. 5(a) and (b) show an example of determination criteria formalfunction detection, which is used in this embodiment. FIG. 5(a) showsan example of a table for malfunction detection. FIG. 5(b) shows arelationship between abnormal current detection threshold value and theabnormal current according to the example of the FIG. 5(a). By referringto the table shown in FIG. 5(a), when a battery capacity (%) largecurrent more than the value shown in the table is detected, it ispossible to determine that a malfunction occurs. For example, as shownin FIG. 5(b), it is possible, as soon as current of 3.3 A flows, todetect that it is an abnormal current. It is also possible, when currentof 2.0 A flows, to determine that there is a malfunction at a time ofbattery capacity of 81%. In any of these cases, since the batterycapacity is less than 100%, and the protection circuit operates when thebattery voltage is 4.20 V/cell or less, any safety problem does notoccur. Regarding the values shown in FIG. 5(a), values of the batterycapacity are represented as integers. Values between the integers may beapproximated, for example, by rounding off.

[0050] Next, processes executed in this embodiment for achievingdetection of abnormal state and protection functions will be described.

[0051]FIG. 6 shows a block diagram of a process executed in the CPU 61of the intelligent battery 52. In this embodiment, it comprises acharging current measurement unit 71 for measuring charging current inresponse to output from the current detection circuit 64, and a batterycapacity integration unit 72 for calculating battery capacity based oncharging current measured by the charging current measurement unit 71,or based on the charging current and voltage from the voltage detectioncircuit 63. The battery capacity integration unit 72 can calculatebattery capacity as electric charge amount (Ah) by integrating currentvalue with respect to time, or battery capacity as electric energy (Wh)by integrating current value multiplied by voltage value, with respectto time.

[0052] In an abnormal current detection table 73, a table, for exampleas shown in FIG. 5(a) is stored. An abnormal current determination unit74 compares value stored in the abnormal current detection table 73 andoutput results from the charging current measurement unit 71 and thebattery capacity integration unit 72, then determines if there is amalfunction. A charging protection FET off instruction unit 75, when theabnormal current determination unit determines that there is amalfunction, cause the charging-stop FET 66 (FET4) to operate to abortthe charging. A malfunction occurrence notification unit 76 is used inresponse to output of a malfunction occurrence from the abnormal currentdetermination unit 74 for notifying the embedded controller 41(system-side) of the occurrence of abnormal state.

[0053]FIG. 7 is a flow chart showing process flow in the case of usingthe table shown in FIG. 5(a). The CPU 61 of the intelligent battery 52at first determines if charging is being performed or not (step 101). Ifcharging is not being performed, then the process stands by, and ifcharging is being performed, then the charging current measurement unit71 measures charging current value (step 102). Then, the batterycapacity integration unit 72 derives integrated capacity (step 103). Theabnormal current determination unit 74 determines if the integratedcapacity is in the range of 0% to 70% (represented as approximationincluding decimals, same for later description), where 100% correspondsto the full capacity (step 104). If the condition is fulfilled, it isdetermined if the current value is 3.0 A or less, or not; if it is 3.0 Aor less, then the process returns to step 101 with recognition ofnormality; if it is more than 3.0 A, then the process goes tomalfunction processing with recognition of malfunction.

[0054] In the malfunction processing, in accordance with the chargingprotection FET off instruction unit 75, charging-stop process isperformed by the charging-stop FET 66 (FET4) that is a protectioncircuit (step 106). Then, the malfunction occurrence notification unit76 notifies the embedded controller 41 (system-side) of the malfunctionoccurrence (step 107). Then, in the system-side, the user is notified ofthe malfunction occurrence by using the LCD 18 (step 108), and themalfunction processing is completed.

[0055] If the condition of step 104 is not fulfilled at the abnormalcurrent determination unit 74, it is determined if the capacity is inthe range of 71% to 80%, or not based on table information stored in theabnormal current detection table 73 (step 109). If the capacity is inthe range, it is determined if the current value is more than 2.5 A(step 110), or not. If the current value is within 2.5 A, then theprocess returns to step 101 with recognition of normality. If thecurrent value is more than 2.5 A, then the process goes to malfunctionprocessing of steps 106 to 108 with recognition of malfunctionoccurrence.

[0056] Similarly, it is determined, based on the table informationstored in the abnormal current detection table 73, if the capacity is inthe range of 81% to 90%, or not (step 111). If the capacity is in therange of 81% to 90%, then it is determined if the current is within 2.0A (step 112), or not. If the current value exceeds 2.0 A, thenmalfunction processing of steps 106 to 108 is performed. Similarly, itis determined if the capacity is in the range of 91% to 95%, or not(step 113). If the capacity is in the range of 91% to 95%, then it isdetermined if the current value is within 1.3 A, or not (step 114). Ifthe value exceeds 1.3 A, then the malfunction processing of steps 106 to108 is performed. Further, similarly, it is determined if the capacityis in the range of 96% to 100%, or not (step 115). If the capacity is inthe range of 96% to 100%, then it is determined if the current value iswithin 0.8 A (step 116), or not. If the current value exceeds 0.8 A,then the malfunction processing of steps 106 to 108 is performed. In theway described above, by sequentially referring to values in a table formalfunction detection, for example as shown in FIG. 5(a), detection ofan abnormal state in the intelligent battery 52 is ensured.

[0057] Next, a detection method for detecting abnormal current by usingnumerical formulas instead of table information as shown in FIG. 5(a),which is stored in the abnormal current detection table 73, will bedescribed. For example, it is possible to derive approximation formulasfrom the relationship between battery capacity and charging current asshown in FIG. 4, and to detect an abnormal state based on theapproximation formulas. For example, from the relationship shown in FIG.4, numerical formulas for detection of abnormal current are derived asfollows:

Y=3100 (mA), for battery capacity X≦70%; and

Y=(60X+6700 (mA), for 71%<battery capacity X≦100%,

[0058] where Y represents abnormal current value, and X representsbattery capacity.

[0059]FIG. 8 is a flow chart showing a process flow for detection ofabnormal state based on numerical formulas described above. In the CPU61 of the intelligent battery 52, at first it is determined if chargingis being performed or not (step 201). If charging is not beingperformed, then the process stands by. If charging is being performed,charging current is measured by the charging current measurement unit 71(step 202), and integrated capacity is obtained by the battery capacityintegration unit 72 (step 203). Then, an abnormal current value iscalculated from the integrated capacity by using the numerical formulasdescribed above (step 204). Then, the abnormal current value obtained atstep 204 is compared with the charging current value measured at step202 (step 205). If the charging current value does not exceeds theabnormal current value, then the process returns to step 201 withrecognition of normal state.

[0060] If the charging current value exceeds the abnormal current valueat step 205, charging is stopped by charging-stop FET 66 (FET4) that isa protection circuit (step 206). Then, the embedded controller 41 insystem-side is notified of malfunction occurrence (step 207). Then, inthe system-side, the malfunction occurrence is notified to the userthrough the LCD 18 (step 208), and the series of processes is completed.

[0061] As described above, in this embodiment, a mechanism for detectingabnormal charging in early stage and aborting the charging, is providedin the battery (intelligent battery 52). Even if the battery cell 62itself has a short-circuit problem, safety for the intelligent battery52 can be ensured unless charging with voltage that exceeds a predefinedvoltage because of abnormal charging is not performed. This embodimentcan provide a system, which is also safer even if a short-circuitproblem in the battery cell 62 itself and a problem of the chargingcircuit in the system-side occur. Additionally, when a malfunction isdetected by the abnormal charging detection mechanism in the batterypack (intelligent battery 52), the charging can be aborted, and theproblem occurrence can be notified to the user by notifying thesystem-side of the problem occurrence.

[0062] The relational characteristic as between battery capacity andcharging current in normal charging, shown in FIG. 4, varies to someextent depending on the type of battery (manufacturer). However, thesystem-side does not need to know difference between the battery typesor the like, since the abnormal current detection table 73 in thebattery includes table information shown in FIG. 5(a), for malfunctiondetection, and the CPU 61 in the battery determines malfunctionoccurrence and activates the protection circuit. The CPU 61 in thebattery pack, upon detection of a malfunction, activates the protectioncircuit (charging-stop FET 66 (FET4)) and notifies the system-side ofthe malfunction occurrence. The embedded controller 41, upon receivingnotification of malfunction occurrence from the battery (intelligentbattery 52), alerts the CPU 11 (the main processor). The CPU 11 that hasreceived the alert can notify the user of the malfunction occurrence bydisplaying the malfunction occurrence on the LCD 18, CRT monitor or thelike. In order to notify the user of malfunction occurrence, flashingLED or beep sound, for example, may be used.

[0063] Finally, an exemplary case will be described wherein the chargerin the main system that is a notebook PC employsconstant-current/constant-voltage charging method, and the externalcharger employs pulse-charging method. The abnormal charging detectionmechanism in this embodiment can not used for a special-type chargerthat performs pulse-charging, for example, for lithium ion battery orlithium polymer battery. Pulse-charging is intended to perform rapidcharging, in which large current flows in pulse form with a chargingvoltage higher than a typical charging voltage. In such a case, when theconfiguration described above is used without any modification, chargingis aborted because it is determined that the charging current of theexternal charger is due to abnormal charging. In order to avoid this, aconfiguration is available, for example, wherein the device connected tothe battery (intelligent battery 52) uses a communication line (COM1)for sending identification information for the device, or ID to the CPU61 inside the battery. When CPU 61 recognizes connection of the batteryto the main system by ID, the abnormal charging detection mechanism inthis embodiment is enabled, and otherwise disabled. Such a configurationallows effective application of this embodiment in a possible case wherethe battery is connected to a charger with different charging modes.

[0064] As described above, the present invention provides a battery,which is safer even if dual accidental malfunctions occur.

What is claimed is:
 1. A power supply system with a battery forsupplying power to a main system, comprising: a charging currentmeasuring unit for measuring charging current for said battery; abattery capacity calculating unit for calculating battery capacity ofsaid battery; and a detecting unit for detecting malfunction occurringin said battery based on a charging current value obtained by saidcharging current measuring unit and said battery capacity calculated bysaid battery capacity calculating unit.
 2. The power supply systemaccording to claim 1, further comprising a protection facilityactivating unit for activating a protection facility based on detectionof malfunction occurrence by said detecting unit.
 3. The power supplysystem according to claim 1, further comprising a notification unit fornotifying said main system of malfunction based on detection of themalfunction occurrence by said detecting unit.
 4. A computer device,comprising: a main system for data processing; and an intelligentbattery for supplying power to said main system, wherein saidintelligent battery comprises: a battery cell for charging anddischarging, a current detection circuit for detecting charging currentfor said battery cell; and a CPU for calculating battery capacity byintegrating charging current detected by said current detection circuit,and recognizing malfunction occurring in the battery based on chargingcurrent value detected by the current detection circuit and thecalculated battery capacity.
 5. The computer device according to claim4, wherein said intelligent battery further comprises a protectioncircuit for performing stop operation according to instruction from theCPU based on recognition of malfunction occurrence by said CPU.
 6. Abattery for supplying power to an electric apparatus, comprising: acharging current measuring unit for measuring charging current for abattery cell; a battery capacity integration unit for integratingbattery capacity for said battery cell; and a malfunction detecting unitfor detecting malfunction occurrence based on a charging current valuemeasured by said charging current measuring unit and battery capacityintegrated by said battery capacity integration unit.
 7. The batteryaccording to claim 6, wherein said malfunction detecting unit detectsmalfunction occurrence based on information in a table for malfunctiondetection showing the relation between battery capacity and malfunctiondetection current value.
 8. The battery according to claim 6, whereinsaid malfunction detecting unit detects malfunction occurrence based onan equation representing the relation between battery capacity andcharging current value, which equation is separately defined accordingto battery capacity.
 9. A battery, comprising: a battery cell; a voltagedetection circuit for detecting voltage for said battery cell; a currentdetection circuit for detecting charging current for said battery cell;a charging stop unit for stopping charging for said battery cell; and acontrol unit for activating said charging stop unit based on voltagedetected by said voltage detection circuit, wherein before the voltagereaches a voltage for activating said charging stop unit, said controlunit detects a malfunction state based on a charging current valuedetected by said current detection circuit, and activates the chargingstop unit.
 10. The battery according to claim 9, wherein said controlunit calculates capacity of said battery cell, and if the chargingcurrent value detected for the calculated capacity by said currentdetection circuit is larger than a normal value, determines that amalfunction has occurred.
 11. The battery cell according to claim 9,wherein said control unit, when connected to an apparatus with a chargeremploying constant-current/constant-voltage charging mode, activatessaid the charging stop unit in response to said detection ofmalfunction.
 12. A method for protecting a battery from abnormalcharging, comprising: measuring a charging current value for saidbattery; calculating integrated capacity for said battery; andactivating a protection facility when the charging current valuemeasured for the calculated integrated capacity is larger than apredetermined value.
 13. The method according to claim 12, wherein theprotection facility is activated based on information specifying areference value representing a charging current value at which amalfunction is detected for an integration capacity.
 14. The methodaccording to claim 12, wherein the protection facility is activated in astate where said integrated capacity is less than 100%.
 15. A method forprotecting an intelligent battery with a microcomputer from abnormalcharging, comprising: recognizing that said intelligent battery isconnected to an apparatus with a charger forconstant-current/constant-voltage charging; measuring charging currentvalue when said intelligent battery is charged while switching fromconstant-current charging to constant-voltage charging; determiningbased on the measured charging current value whether abnormal chargingoccurs or not; and aborting charging when it is determined that abnormalcharging occurs.
 16. The method according to claim 15, wherein theconnection to said apparatus is recognized by receiving the ID of saiddevice.
 17. The method according to claim 15, wherein when it isdetermined that abnormal charging occurs, said apparatus is notified ofthe occurrence of abnormal charging.
 18. A program of software-basedcode for enabling a microcomputer contained in a battery to perform: acharging function for measuring charging current value for said battery;a calculating function for calculating integrated capacity in saidbattery; and a protecting function for activating a protection facilitywhen the charging current value measured for the calculated integratedcapacity is larger than a predetermined value.
 19. A program forenabling a microcomputer contained in a battery to perform: a functionfor recognizing that said battery is connected to an apparatus with acharger for constant-current/constant-voltage charging; a function formeasuring charging current value when said battery is charged whileswitching from constant-current charging to constant-voltage charging; afunction for determining based on the measured charging current valuewhether abnormal charging occurs or not; and a function for abortingcharging when it is determined that abnormal charging occurs.